The present invention relates to interior panels for automotive vehicle doors, and more particularly to improvements in apparatuses and techniques for forming interior panels by which the incidence of panel surface defects is minimized.
An interior panel for an automotive vehicle door typically includes an exterior layer, or skin, made from a smooth, imperforate material, such as vinyl film, backed by a relatively rigid substrate. The panel may be formed in a vacuum mold assembly, the exterior layer being vacuum-drawn in a heated state to the molding surface of a lower, or female, mold part. The molding surface defines the exterior, or A-side, surface of the panel. The substrate material is then applied to the back of the exterior layer, typically by adhering a rigid pre-formed substrate panel to the vacuum-formed exterior layer, or by pouring a foamable liquid onto the vacuum-molded exterior layer disposed in the lower vacuum mold part. A cooperating upper, or male, mold part, also known as a core, is engaged with the lower mold part to press the pre-formed substrate panel to the exterior layer or to form and cure the foamed material onto the back of the exterior layer. The upper mold part has a molding surface which defines the back, or B-side, surface of the panel. A reinforcing material in the form of a mat may be embedded into the substrate when it is pre-formed or when it is formed directly onto the back of the exterior layer to enhance the strength and durability of the substrate.
The exterior surface of the exterior layer may have embossments and/or surface texture formed therein by the molding surface of the lower mold part. In addition, the interior panel may include other features, such as an arm rest, door handle, openings for door release levers and accessories, such as door speakers and interior lights, and fabric or carpet bolsters attached to the exterior surface of the panel during or after the panel-forming process.
Various methods for forming an interior panel for a vehicle door are described in the prior art literature, and particular methods are described in U.S. Pat. Nos. 5,571,355; 5,397,409; and 5,387,390, the contents of which are hereby incorporated by reference.
In one process described in the previously-mentioned patents, a heated sheet of vinyl laminate material is laid in the lower mold part of a vacuum mold assembly. The vinyl laminate includes an outer layer comprised of a smooth, relatively imperforate vinyl sheet and a back layer of relatively soft foam material bonded to the back side thereof. A vacuum is applied at the molding surface of the lower mold part to draw the vinyl sheet to the molding surface. In a subsequent step of the panel-forming process, a fiberglass reinforcing mat is laid in the lower mold part on top of the vacuum-drawn vinyl layer. After vacuum-drawing the vinyl layer, a foamable material, such as a foamable polyurethane liquid, is poured into the lower mold part on top of the fiberglass reinforcing mat and the vacuum-drawn vinyl layer. A cooperating upper mold part, having a molding surface which defines the back of the panel, is moved into cooperating engagement with the lower mold part, with the vinyl layer, the fiberglass reinforcing mat, and foamable material disposed between the respective molding surfaces of the upper and lower mold parts. The foamable material is foamed and cured under heat and pressure, resulting in a relatively rigid substrate of foamed material with the fiberglass reinforcing material embedded therein. The resulting panel has a vinyl exterior surface backed by a relatively rigid, reinforced substrate of greater thickness than the vinyl exterior surface.
With prior art vacuum forming techniques, the exterior vinyl layer, being an essentially imperforate material, responds to the applied vacuum and is drawn to conform to the molding surface of the lower mold part. The fiberglass reinforcing mat, however, is not imperforate, and therefore, the mat does not respond to the applied vacuum so it is not drawn into tight conformity with the vinyl layer. This is especially true near portions of the molding surface that include deep draws and steep gradients, such as depressions for forming an arm rest portion of the panel. Accordingly, the reinforcing mat is not secured to the back, or B-side, of the vinyl layer and areas of the mat may not even be urged into close conformity with the vinyl layer, even when engaged by the second mold part, because the mat is embedded in the substrate material which is thicker than the mat. Thus, the reinforcing mat may float into the substrate material before the substrate material is cured, thereby creating gaps between the reinforcing mat and the vinyl layer which will fill with substrate material.
When a substrate material, such as urethane, expands during the foaming process, it gives off carbon dioxide (CO.sub.2) gas. One of the functions of the fiberglass reinforcing mat, in addition to reinforcing the substrate, is to act as a mechanical barrier to prevent gas bubbles created in the substrate from reaching the vinyl layer and pushing to the A-side of the vinyl where they can create surface defects in the panel. If the fiberglass mat separates from the vinyl layer, the expanding substrate material that fills the gaps between the mat and the vinyl can create gas bubbles which can migrate unimpeded to the A-side of the panel. This is known in the industry as an "overgas condition". Accordingly, even though prior art door panel-forming techniques call for the provision of a reinforcing mat, panel surface defects can occur due to overgas conditions because there is no mechanism by which gaps between the reinforcing mat and the vinyl layer are reliably prevented.